An electrode base material and a noble metal tip are welded by laser welding at a center electrode and a ground electrode of a spark plug in some cases. In laser welding of the electrode base material and the noble metal tip, a so-called “welding droop” where a surface of a fusion portion extends may reach a front end of the noble metal tip, or metal melted by laser irradiation may sputter and adhere to the electrode base material and the noble metal tip. Such welding droop and spatter may lower the ignitability of the spark plug. Further, if a blow hole occurs at the fusion portion during laser irradiation, the joining strength of the fusion portion may be lowered and the noble metal tip may be peeled off from the electrode base material. WO 2008/123343 discloses a technique for suppressing the generation of the spatter, the blow hole, or the like by changing a laser intensity waveform of a rectangular shape used for laser welding.
Recently, a noble metal tip having a higher melting point is used because the temperature of the environment where a spark plug is used is increased and the improvement of the ignitability is desired. When a high energy laser is used to weld an electrode base material and a noble metal tip having a high melting point, a welding droop, a spatter, and a blow hole are more likely to occur. Thus, a technique for further suppressing the welding droop, the spatter, and the blow hole has been desired.
The present invention has been made to solve the above-mentioned problems, and can be achieved as the following embodiments.